With remarkable advance of industrial activities, it has been strongly feared that carbon dioxide artificially emitted would cause environmental destruction on a global scale. Especially, since a vast amount of carbon dioxide is emitted from power generation systems using fossil fuel, it is necessary to control carbon dioxide emission to the atmosphere.
In order to control carbon dioxide emission to the atmosphere, researches have been conducted in various places. New Energy and Industrial Technology Development Organization (NEDO) has been researching a closed gas turbine power generation system with high power generation efficiency, for the purpose of reducing the amount of carbon dioxide emitted from power generation systems.
The gas turbine power generation system being researched in the NEDO is configured such that a steam turbine is connected to a closed-cycle gas turbine having a methane and oxygen combustor on the same shaft. The methane and oxygen combustor is configured to heat steam discharged from a high-pressure steam turbine, and a high-temperature gas turbine uses the steam as a drive gas. Thereafter, a part of the steam is extracted and supplied to a low-pressure steam turbine.
While the most part of carbon dioxide generated in the methane and oxygen combustor circulates within the gas turbine, carbon dioxide flowing along with the steam supplied to the low-pressure steam turbine is separated in a water condenser and then compressed by a compressor. The compressed carbon dioxide can be stored and fixed by a proper method.
In the manner as stated above, the closed gas turbine system can facilitate collecting carbon dioxide. But, in order to achieve this, high technology is necessary, and the closed gas turbine system is currently developed.
A collected carbon dioxide disposal method employed in this novel system has not been clarified. As a promising method of collecting carbon dioxide emitted from thermal power plants without releasing the carbon dioxide to atmosphere as a greenhouse gas, it is known that liquefied carbon dioxide is sequestrated in sea bottom or in underground water layer. Although it is expected that a vast amount of carbon dioxide can be sequestrated in the sea bottom, attention should be given to a possibility that the liquefied carbon dioxide is re-released to atmosphere for a long time period, for example, for several ten years or several hundred years.
Meanwhile, in order to meet an increasing demand for the energy, various energy sources have been developed, among which, gas contained in coal beds has been noticed. Coal beds exist throughout the world, and a vast amount of coal is buried therein. A vast amount of gas containing methane as major component is stored in the coal beds as coal bed methane. However, conventionally, in order to avoid danger in mining, the coal gas is released before mining. And, the coal gas is ventilated by air fed to cavities and emitted to atmosphere, or used as fuel in coal mining sites.
It is known that a vast amount of coal gas is adsorbed in the coals, and the coal gas is released when the coals are exposed in atmosphere or fluid is fed under pressure into the coal beds. Accordingly, it is considered that methane is collected from coal beds which are now incapable of being mined, or are too costly to be mined.
Further, the coal beds are promising as carbon dioxide gas sequestrating places, since the coal beds exist underground and carbon dioxide is adsorbed in and fixed to the coal beds.